You can reuse the gasket over and over again..I do...unless you rip it obviously....Gas doesnt get that high in the bowls....

-is your carb an original? or aftermarket federal/edelbrock?

098 /095 is about right for stock 340 carb....
factory settings always had smaller secondary jet...never bigger...

You however are running bigger cam and headers...that will automatically lean out a factory setting carb....How do your plugs read?

Check your jets --the numbers are on them..or take numbered drill bit to check....

You want more HP for your set up? GO to a 750 AVS or AFB....(they dont actuall flow 750 cfm but less)..You will keep same gas mileage and get 10-15hp boost...You are running too small a carb for a hopped up 340...